The influence of the inactivating agent on the antigen content of inactivated Newcastle disease vaccines assessed by the in vitro potency test

An in vitro potency test has recently been included in the European Pharmacopoeia (EP) monograph (01/2007:0870) to assess the potency of inactivated Newcastle disease (ND) vaccines. This enzyme linked immunosorbent assay (ELISA) is an attractive alternative for the existing in vivo potency tests especially with regard to the objective of the European Authorities to Replace, Reduce and Refine the use of laboratory animals for production and quality control of immunobiologicals.In the present study the influence of the inactivant on the antigen content established by ELISA was evaluated. Therefore, oil based vaccines containing similar concentrations of β-propiolactone (BPL) or formaldehyde inactivated Newcastle disease virus (NDV) were examined by ELISA and in the in vivo potency tests outlined in the EP.The results obtained demonstrate that the use of formaldehyde as inactivant lowered the in vitro potency compared to BPL as inactivant. In contrast, the in vivo potency was not affected. Therefore, the ELISA should not be used to compare the potency of commercial ND vaccines containing formaldehyde inactivated NDV with those containing BPL inactivated NDV. However, the ELISA is considered an attractive alternative for the existing in vivo potency tests since it can be used by vaccine manufacturers for the release of inactivated ND vaccines.